Magnetic decelerator for projectiles and system of deceleration and recovery thereof

ABSTRACT

A magnetic decelerator for projectiles and system of deceleration and recovery providing for economically recovering the projectiles undamaged. The projectile includes a magnetic permeable slug or the like of predetermined shape and size formed therein. A magnetic field is created between north and south pole pieces having electrically conductive facings thereon. As the projectile and slug therein pass between the pole pieces the movement of the slug through the magnetic flux lines induces ring currents in the conductive pole piece facings, which cause the deceleration and dissipation of energy of the projectile.

ilnited States Patent Harris et al.

[ 1 Dec. 24, 1974 MAGNETIC DECELERATOR FOR 3,337,760 8/1967 Allport 310/13 PROJECTKLES AND SYSTEM OF DECELERATION AND RECOVERY Primary ExaminerDonovan F. Duggan THEREOF Attorney, Agent, or Firm-Saul Elbaum [75] Inventors: Fred T. Harris, Rockville, Md.;

Edwin L. Resler, Jr., Ithaca, NY. [73] Assignee: The United States of America as [57] ABSTRACT represented P the Secretary of the A magnetic decelerator for projectiles and system of Army Washmgton, deceleration and recovery providing for economically [22] .Filed: June 4, 1971 recovering the projectiles undamaged. The projectile includes a magnetic permeable slug or the like of pre- [21 1 Appl' 149,965 determined shape and size formed therein. A magnetic field is created between north and south pole pieces 52 US. Cl. 310/13, 335/268 having electrically conductive facings thereon As the 51] Int. Cl. H02k 49/00 projectile and Slug therein P between the P [58] Field of Search 310/12-19; Pieces the movement of the Slug through the magnetic 335/263 flux lines induces ring currents in the conductive pole piece facings, which cause the deceleration and dissi- 5 References Cited pation of energy of the projectile.

UNITED STATES PATENTS 4 Claims, 2 Drawing Figures 3.300.744 1/1967 Deutsch 3l0/l4 X Patented Dec. 24, 1974 COPPE 1? .Sm/P

COPPER .5 7P0 BY 2M Jamie/MW ATTORNEYS MAGNETIC DECELERATOR FOR PROJECTILES AND SYSTEM OF DECELERATION AND RECOVERY THEREOF ORIGIN OF THE INVENTION The invention described herein may be manufactured, used and licensed by or for the United States Government for governmental purposes without the payment to us of any royalty thereon.

BACKGROUND OF THE INVENTION The present invention is related to projectile saving by decelerating and stopping projectiles with the aid of magnetic field braking means.

The-operation of the system of the present invention is based on Lenzs law which states that in electromagnetic induction the direction of the induced current is such that the change in flux due to it is opposite in direction to the change in flux which produced the induced current.

In the system of the present invention the principles of Lenzs law are utilized to create a decelerating force on a projectile passing through a static magnetic field.

It is an object of the present invention to provide a system of magnetic deceleration for projectiles and for recovery of such decelerated projectiles without damage.

Another object is to provide a novel system of decelerating projectiles, whereby the system provides for control over a wide range of velocities substantially free of damage to the projectile and further is economical in practice.

FIG. 1 is a diagrammatic illustration of a static magnetic field generator having north and south pole members with a magnetic permeable slug loaded projectile passing through the field at a given velocity; and

FIG. 2 is a diagrammatic view partly in perspective with one pole piece removed to illustrate the effects of the movement of a rectangular slug of magnetic permeable material through the static magnetic field.

Referring in detail to the Figures of the drawing, there is shown a closed static magnetic circuit with provision to provide an induced current to set up a magnetic field of its own within an area bounded by pole pieces and 11. The pole pieces are faced, for example, with copper conductors l2 and 13. Pole piece 10 may be designated the north pole and the pole piece 11 the south pole.

The magnetic circuit may be energized by any suitable electric source or from permanent magnet means. The poles of the magnetic circuit means set up a magnetic field coactive with a magnetic permeable slug 16 carried by a projectile of a velocity V. This slug carrying projectile passes between the pole pieces 10 and 11 with the respective copper strip portions 12 and 13 and sets up ring currents in the copper strip portions, as illustrated in FIG. 2.These ring currents generate a decelerating force for stopping the projectile.

Thus, as above stated by Lenzs law, it is known that the direction of an induced current is such as to oppose the cause producing it. Accordingly, with a closed static magnetic circuit defining an original magnetic field between pole pieces 10 and 11, an induced current set up in copper strips 12 and 13, as the magnetic permeable slug 16 passes through the field, creates an induced magnetic field directed (a) opposite to the original field if said original field is increasing but, (b) in the same direction of the original field if this field is decreasing. Therefore, it is the change in flux in the projectile passing through the field of the static circuit, not the flux itself which is opposed by the induced current.

In order to have an induced current, there must be a closed circuit and to avoid cancellation of the total voltage around the current path, one side of the circuit loops, shown in FIG. 2, should be outside of the changing magnetic field.

As an example of an optimum operation, consider the rectangular permeable metal slug 16 as a projectile having a velocity V, shown in FIG. 2, passing the magnetic field B between the two pole pieces 10 and 11 faced with a good conductor such as copper plates 12 and 13 of a thickness t. The area of the, projectile slug 16 containing the flux is bh.

The force on the copper strips l2, 13, the decelerating force, can be computed in the same way one can compute the force, F, on a wire from the relationship:

where I the current through the strips B magnetic field density in Wlm and h length of current path in m.

The current, I, can be determined from the relationship I e/R, where e induced voltage and R resistance.

The induced voltage, 1:, can be calculated from the equation 6 VBh where V velocity in m/sec.

The resistance, R, can be determined from the equation HR bt/2h, where 0 conductivity in mho/m, hr area of conducting path in m, and 2h total current path length assuming h b in FIG. 2.

Therefore I e/R V B a!) t (Neglecting inductance and skin depth effects) F I B h V 13 ch b t for each copper strip The force decelerating a 4 inch projectile at m/sec is for b l/l6 inch h 4 inches t 11 inch B k w/m V= 100 m/sec.

I B h 630 newtons or 143 lbs. for each copper strip.

Total force is then 1,260 nt or '286 lbs.

Numerous experiments have proven the variable controllable possibilities of the present novel system structure and method by using variable permeable slug materials and of slugs with different shapes and for providing variable control of stopping distances for projectiles of varying velocities. However, the basic principles herein involved are believed apparent from the foregoing description and illustrations.

Thus the control of the projectiles may be for low or relatively high velocities; and as the velocity of the projectile increases the decelerating force will become maximum, if the other parameters are constant.

It should be understood that the invention is not limited to the exact details of construction shown and described herein for obvious modifications will occur to persons skilled in the art.

tive facings due to the interaction of said magnetic field and said slug passing therethrough.

2. A system according to claim 1, wherein said conductive faces are copper.

3. A system according to claim 1, wherein said slug is rectangular in shape.

4. A system according to claim 1 wherein a portion of said ring currents pass through said faces in the area ofsaid slug. 

1. In a system for decelerating a projectile moving along a path at a given velocity, in combination, a magnetic-permeable slug carried by said projectile; means for generating a magnetic field in a substantially transverse direction to said path, said means including north and south pole pieces having substantially planar parallel surfaces disposed on opposite sides of said path; and conductive facing means on said planar surfaces for producing a deceLerating force on said projectile in response to ring currents induced in said conductive facings due to the interaction of said magnetic field and said slug passing therethrough.
 2. A system according to claim 1, wherein said conductive faces are copper.
 3. A system according to claim 1, wherein said slug is rectangular in shape.
 4. A system according to claim 1 wherein a portion of said ring currents pass through said faces in the area of said slug. 